1. Field of the Invention
The present invention relates to a wheel suspension type front fork of bicycles or other two-wheeled vehicles and a manufacturing method of a sliding tube constituting the front fork.
2. Description of the Related Art
Bicycles or the like adopt the wheel suspension type front fork in order to absorb a shock when a front wheel runs on a difference in level.
FIGS. 6(a) and (b) illustrate an example of a conventional wheel suspension type front fork. The front fork includes a sliding tube 1 having an upper portion which is fit slidably to a supporting tube not shown and a lower portion which is formed with a thick axle receiver 2 including a recess for supporting an axle of the front wheel. A step 3 is formed on an inner periphery at a lower portion of the sliding tube 1 and a disklike receiving plate 4 is engaged on the step 3. A lower end of a coil spring 5 abuts against the receiving plate 4 and an upper end of the coil spring 5 abuts against a spring receiving member (not shown) which is fit and fixed to a lower portion of the supporting tube. The coil spring 5 and the receiving plate 4 constitute a portion of a shock absorber. Accordingly, the force of shock can be absorbed by moving up and down the sliding tube 1 by expansion and contraction of the coil spring 5.
FIGS. 7(a) and (b) illustrate an example of another conventional wheel suspension type front fork. A sliding tube 1 of the front fork includes a tube portion 6 and an axle receiving portion 7. An upper cylindrical portion of the axle receiving portion 7 is fit into a lower portion of the tube portion 6 and joined thereto with adhesive or by brazing.
With the front fork shown in FIG. 6, the sliding tube 1 is integrally formed to the axle receiver 2 by means of casting or forging and the step 3 for supporting the receiving plate 4 is formed by cutting the inner surface of the sliding tube 1. Accordingly, the conventional front fork requires an expensive metal mold and associated facilities as well as the cutting technique accompanied with difficulties in work. Thus, the front fork itself is very expensive.
Further, with the front fork shown in FIG. 7, since a metal mold and associated facilities for casting or forging are required similarly in order to form the axle receiving portion 7, the front fork is expensive, and since there is a possibility that the axle receiving portion 7 is separated from the tube 6 when the force of shock is added, it is necessary to secure the joining strength thereof and accordingly the joining work requires much labor and attention.
In addition, in the front fork shown in FIGS. 6 and 7, every time the design and specification thereof are modified, a metal mold must be provided and the cost of equipment is increased.